Inkjet printing method and apparatus with feedback control

Abstract

An inkjet printing method and system includes an arrangement that is adapted to repair a printed image using a combination of in-line imaging and feedback control of an inkjet printhead or printing with a redundant inkjet printhead. The inkjet printing method and system is further adapted to print at higher optical density than is normally possible by use of multi-pass capabilities.

What is claimed is: 
     
       1. A method of printing comprising the steps of:
 transporting media in an initial print pass to an inkjet printhead; 
 using the inkjet printhead to print an image on the media by applying ink from nozzles on the inkjet printhead onto said media; 
 inspecting the printed image on the media to detect a presence of at least a streak in said printed image caused by at least one defective nozzle in said inkjet printhead; 
 transporting the media with the printed image thereon in an additional print pass back to said inkjet printhead if a streak is detected on said printed image; 
 adjusting a cross track position of one of the media or the inkjet printhead relative to the other of the media or the inkjet printhead to position a non-defective nozzle of the inkjet printhead over the detected streak; and 
 applying ink from the non-defective nozzle to an area of the printed image corresponding to the detected streak to repair the streak in said printed image. 
 
     
     
       2. A method according to  claim 1 , further comprising:
 processing the printed image if a streak is detected to determine a location of the detected streak relative to an edge of the printed image on the media, such that said adjusting step adjusts the cross track position of the one of the media or the inkjet printhead relative to the other of the media or the inkjet printhead in accordance with the determined location of the detected streak. 
 
     
     
       3. A method according to  claim 1 , wherein said inspecting step comprises scanning the printed image on the media to detect the presence of the streak. 
     
     
       4. A method according to  claim 1 , wherein the media with the printed image thereon is not transported back to said inkjet printhead for said additional print pass if a streak is not detected on the printed image. 
     
     
       5. A method according to  claim 4 , wherein the media is transported past said inkjet printhead in the same direction during the initial print pass and the additional print pass. 
     
     
       6. A method according to  claim 5 , wherein for subsequent media, the cross-track position of one of the media or the inkjet printhead relative to the other of the media or the inkjet printhead is adjusted such that the defective nozzle is aligned with a non-print region of the image. 
     
     
       7. A method according to  claim 1 , wherein said step of transporting the media with the printed image thereon in the additional print pass back to said inkjet printhead if a streak is detected on said printed image comprises transporting the media with the printed image thereon in a cyclical path to a position upstream of the inkjet printhead with respect to a direction of travel of said media. 
     
     
       8. A method according to  claim 1 , wherein the printed image has a target print density, and wherein the inspecting step further comprises detecting a print density of the printed image, such that the method further comprises:
 transporting the media with the printed image thereon back to said inkjet printhead if the detected print density is below the target print density; and 
 using said inkjet printhead at least one more time to print a second image on top of the first image, wherein at least a portion of the second image is the same as the first image to thereby raise the print density. 
 
     
     
       9. A method according to  claim 1 , wherein said media is transported on an endless belt. 
     
     
       10. A method according to  claim 9 , further comprising charging the endless belt to hold the media on the belt during transport through electrostatic adhesion. 
     
     
       11. A method according to  claim 1 , wherein said ink is a aqueous based ink. 
     
     
       12. A printing apparatus comprising:
 an inkjet printhead adapted to print an image on media by applying ink from nozzles on the inkjet printhead onto the media; 
 an image capture device adapted to inspect the printed image on the media to detect a presence of at least a streak in said printed image caused by at least one defective nozzle in said inkjet printhead; and 
 an adjustment device adapted to adjust a cross track position of one of the media or the inkjet printhead relative to another of the media or the inkjet printhead if a streak is detected on said printed image by said image capture device to position a non-defective nozzle of said inkjet printhead over the detected streak, so that ink from the non-defective nozzle can be applied to an area of the printed image corresponding to the detected streak to repair the detected streak in said printed image. 
 
     
     
       13. A printing apparatus according to  claim 12 , further comprising:
 a media conveying device adapted to convey the media along a media transport path pass said inkjet printhead during a first print pass to print the image on the media, and recirculate the printed image having a streak detected thereon back to the inkjet printhead for a second print pass for the repair of the detected streak. 
 
     
     
       14. A printing apparatus according to  claim 12 , wherein the image capture device is a scanner adapted to scan the printed image on the media. 
     
     
       15. A printing apparatus according to  claim 14 , wherein the scanner is located along the media transport path downstream of the inkjet printhead with respect to a direction of travel of said media, and the conveying device is adapted to return the media back to the inkjet printhead for the second print pass or eject the media with the printed image thereon. 
     
     
       16. A printing apparatus according to  claim 13 , wherein the conveying device comprises an endless belt to which the media is secured for transport. 
     
     
       17. A printing apparatus according to  claim 16 , wherein the media is secured to the endless belt by electrostatic forces. 
     
     
       18. A printing apparatus according to  claim 12 , wherein said ink is an aqueous based ink. 
     
     
       19. A printing apparatus according to  claim 17 , further comprising a discharging unit which can selectively decrease the electrostatic forces holding the media to the endless belt. 
     
     
       20. A printing apparatus according to  claim 16 , further comprising an air jet array directed at the endless belt where the endless belt wraps partially around a roller that guides the endless belt. 
     
     
       21. A printing apparatus according to  claim 17 , wherein the electrostatic forces securing the media to the endless belt are higher at the lead edge of the media than in other portions of the media. 
     
     
       22. A printing apparatus according to  claim 12 , wherein the media includes a boundary which surrounds a printing region, such that printing only occurs in the printing regions.